1. Field of the Invention
The present invention relates to an intaglio printing method, in particular, an intaglio printing method suitable for the formation of spacers for use in a touch panel, an intaglio printer for carrying out the intaglio printing method, and also a touch panel.
2. Discussion of Background
Currently employed touch panels are electrostatic touch panels, optical touch panels, and resistance-type touch panels. Of these touch panels, resistance-type touch panels are most in general use.
A resistance-type touch panel is constructed of a pair of transparent panels or sheets which face each other, provided with a transparent electrode layer such as an ITO layer on the facing side of each panel or sheet. Thus, the touch panel is composed of a pair of such transparent panels or sheets. However, when such a touch panel is used by superimposing the same on a liquid crystal display or a CRT display, a panel made of glass is usually used as the lower panel, and a panel made of a polycarbonate or PET film with a thickness of hundred several tens microns is usually used as the upper panel since it is usually necessary that the upper panel be flexible and be brought into close contact with the lower panel when the upper panel is depressed. The upper most surface of the upper panel made of such a polycarbonate film or a PET film with which is depressed with the fingers or pens is usually coated with a hard coat layer to impart durability to the upper panel.
Coating patterns of transparent electrodes such as ITO electrodes can be roughly classified into two types, a digital type and an analog type.
In the digital type transparent electrodes, long narrow transparent electrodes, divided in the shape of stripes, with the formation of slits therebetween, are formed crosswise on the upper and lower panels, so that when the upper panel is depressed and the transparent electrodes in the upper and lower panels are electrically connected, the connected point or position is detected as a positional data in a horizontal direction and a vertical direction. In the transparent electrodes of the above-mentioned digital type, the position can be identified by detecting the ON/OFF of the stripe-shaped, crosswise disposed transparent electrodes, so that the detection can be performed with high accuracy since no detection error is caused by variations in the value of the resistance of the transparent electrodes, which may be caused by non-uniform coating of the electrodes. However, it is necessary that the transparent electrodes be divided and insulated in the shape of stripes by the formation of a masking resist by photolithography and an etching treatment. Thus, the production cost of the thus divided electrodes is high. Furthermore, the resolution of the electrodes is limited by the degree of the division of the electrodes, so that the digital type transparent electrodes have the shortcoming that the digital type electrodes are not suitable for precise positional detection.
In contrast, in the analog type transparent electrodes, which are recently widely used, the electrodes are not divided, but are continuous in the entire surfaces on the panels. In the transparent electrodes of the analog type, electric current flows in one direction, for instance, in a horizontal direction, through the electrode on a first panel, while in the electrode on a second panel, electric current flows in a direction vertical to the current flow direction in the electrode of the first panel. The upper and lower transparent electrodes are electrically connected by an electroconductive pads at the upper and lower end portions or the left and right end portions of the two electrodes.
When one point of a touch panel comprising the above-mentioned analog type transparent electrodes is depressed, a resistance is determined in proportional to the distance between the depressed point and the position of the pad which may be at the upper or lower end portion, or at the left or right end portion of the electrode. Based on a calculation of the thus determined resistance, the coordinates of the position can be calculated. In comparison with the digital type transparent electrodes, the analog type transparent electrodes, for which slit-shaped division of the electrodes are unnecessary, are capable of detecting the position more precisely. However, in the analog type transparent electrodes, if non-uniformity of the thickness of the coating of the electrodes is large, the precision of the positional detection is significantly lowered, so that a highly accurate control technique is required, for instance, for the vacuum deposition of ITO for the fabrication of the analog type transparent electrodes.
If the coating thickness of the electrodes varies, the actually depressed position differs from the calculated position. Even if any of the electrodes includes one portion in which the coating thickness of the electrode is not uniform, the accuracy of the positional detection is lowered in all the positions in the direction of the flow of the current, so that if there is a plurality of portions in which the coating thickness of the electrode is not uniform, all of the errors in the course from the pad to the contact point accumulate, the accuracy of the positional detection is worsened.
Recently, a hybrid type touch panel has been proposed, in which the advantage of the digital type electrodes that the production thereof is easy, and the advantage of the analog type electrodes that highly precise positional detection can be carried out are combined. In the hybrid type touch panel, the touch panel is divided into relatively large sections with slits being formed therebetween like digital type transparent electrodes, and within each section, analog positional detection is carried out, so that while the high accuracy of the positional detection is maintained in each section, the accumulation of the errors caused by the non-uniformity of the resistance beyond the sections is avoided. By this hybrid type touch panel, the accuracy of the positional detection is significantly improved, but the hybrid type touch panel has the shortcoming that the production cost thereof is extremely high.
In pursuing high precision in the positional detection, the positional detection systems have been changed as mentioned above. One of the most important elements that have significant effects on the cost and the accuracy of the positional detection in such detection systems is a spacer.
The spacer in the touch panel has the function that when the touch panel is not depressed, a predetermined space is maintained between the upper and lower transparent electrodes to avoid unnecessary connection of the two electrodes, while when the touch panel is depressed, the connection of the two electrodes is easily allowed, but the connected area is limited to a proper area.
The touch panel is required to be transparent because in many cases, the touch panel is used on a liquid crystal display or a CRT display. As a matter of course, the spacer for use in the touch panel is also required to be transparent. Therefore, as the material for the space, transparent resins are usually used. Furthermore, in order to improve the security and precision of the detection, and to make the spacer invisible to the eyes, it is required to make the spacer as small as possible in size.
There are two methods for producing the spacer, a printing method and a photolithographic method.
In the printing method, round holes are made in a stainless plate by etching, or round holes are made in a nickel plate by electroforming. By use of the thus produced stainless plate or nickel plate with round holes as a printing mask, for instance, an ultraviolet-curing resin is printed on a panel serving as a print receiving material, whereby a spacer is produced. As the printing masks used in such a printing method, such an etching mask and an additive mask made by electroforming can be employed. Each mask has its own advantages and disadvantages.
The production cost of the above-mentioned etching mask is lower than that of the additive mask. However, as to the shape of the openings of the holes, the inside wall of the holes in the etching mask is rough and the holes are made by etching from the upper side as well as the lower side of the plate, so that a central portion of the through-hole is narrower than the opposite openings of the through-hole. The roughness of the inner wall and the narrowness of the central portion of each hole significantly hinder the passing of the resin that through the hole in the course of the printing process, so that it may occur that the holes are clogged with the resin because the resin stays in the holes, or when the printing mask is separated from the panel serving as a print receiving material, the resin is pulled by both the panel and the mask to become like a thread extended between the the panel and the mask.
When the resin does not easily pass through the holes, as a matter of course, it is difficult to perform printing, using such small holes, so that the etching mask is not suitable for the production of a precise touch panel. Such clogging of the holes with the resin causes defects in the spacer. The result is that if there is one defect in the spacer, the area which is not supported by the spacer increases 4 times, so that the sensitivity of the touch panel becomes significantly non-uniform. Furthermore, if the above-mentioned threading takes place, even if the touch panel is depressed, proper electric connection cannot be performed by the presence of a thread-shaped resin between the upper and lower panels, which also causes non-uniformity in the touching sensitivity of the touch panel.
Because of the above-mentioned problems of the etching mask, there is a tendency that the additive mask is used more than the etching mask for the printing of the spacer.
The additive mask, however, has the shortcoming called hole losing.
The additive mask is produced as follows: A dry film, which is a photoresist, is laminated on a substrate which is an electrode for electroforming, with the application of pressure thereto by a roll. A photo film having a pattern of the same holes as the holes to be formed is brought into close contact with the laminated dry film, exposed to light and developed, whereby a female die for electrolytic plating is formed. The substrate provided with the female die is immersed in an electrolytic plating liquid and a plating layer is caused to grow with shaking to prepare an additive mask with a predetermined thickness. In the case of extremely small holes for preparing a space for the touch panel, the diameter of the female die in the dry film is about several ten microns, and the dry film is often peeled away from the substrate when shaken in the electrolytic plating liquid, which causes the hole losing. This occurs so frequently that it is a big problem when producing the spacer.
It is also difficult to prepare holes in a uniform shape either by the etching mask or by the additive mask, so that the amount of the resin to be printed becomes varies. This makes the height of the spacer non-uniform and makes it difficult to prepare a high precision spacer.
In accordance with the degree of positional detection accuracy and the resolution, there are a touch panel for finger touch, having a relatively large detection area suitable for the depression with the finger, and a touch panel for pen touch, suitable for detecting small characters or icons, using a special pen. AS mentioned above, the spacers prepared by the above-mentioned printing methods are not suitable for detecting small characters or icons, and therefore are currently used in the touch panel for finger touch.
A further method for forming the spacer is a photolithographic method. In the photolithographic method, a photosensitive resin is directly coated on the surface of a transparent electrode provided on the lower panel, and a photo film having a pattern of the same shape as that of the spacer to be formed is superimposed on the coated photosensitive resin, exposed to light and developed, and the remaining photosensitive resin is used as the spacer as it is.
This method is capable of forming a much finer spacer in comparison with the above-mentioned printing method, and the spacer produced by this method is mainly used in portable computer terminals for pen touch. In this method, most of the photosensitive resin is removed as a waste material at the process of the development, so that the production cost including the cost of the material to be removed, and the cost for treating the material to be discarded, are high.
Furthermore, a problem that the spacer falls off the panel due to the insufficient adhesion of the spacer to the panel also takes place.
As the material for the spacer for such a touch panel, rigid plastics are often used. In such a case, the spacer tends to become a lens-shaped spacer due to the surface tension of the plastics. Therefore, load and stress are concentrated on a top portion and the spacer eventually is broken into small particles or powder due to the fatigue thereof. When this takes place, the plastics powder is scattered on the surface of the transparent electrode around the spacer, and works as an insulating, foreign material, and causes a problem that correct and proper positional detection becomes impossible when the touch panel is depressed. Furthermore, the height of the space changes due to the broken spacer, and input errors may also be caused.
It is therefore a first object of the present invention to provide an intaglio printing method suitable for the formation of a spacer with high printing precision for use in a touch panel at low cost, which has excellent reliability free of fatigue destruction and the problem of the falling off from the surface of a print receiving material such as the surface of a panel, and other conventional problems.
A second object of the present invention is to provide an intaglio printer which can carry out the above-mentioned intaglio printing method.
A third object of the present invention is to provide a touch panel of which spacer has high durability.
The first object of the present invention can be achieved by an intaglio printing method for transferring a resin to a print receiving material, using an intaglio printing master having portions depressed in a printing shape below the surface of the printing master, comprising the steps of:
filling a resin paste that can be hardened to a solid resin in the depressed portions of the printing master,
bringing the printing master, with the resin paste being filled in the depressed portions thereof, into close contact with the print receiving material,
hardening the resin paste to make the resin paste a hardened solid resin in the depressed portions of the printing master, and
separating the printing master from the print receiving material so as to transfer the hardened solid resin in the depressed portions of the printing master to the print receiving material.
The first object of the present invention can also be achieved by an intaglio printing method for transferring a resin to a print receiving material, using an intaglio printing master having portions depressed in a printing shape below the surface of the printing master, comprising the steps of:
filling a photo-setting resin paste that can be cured to a photo-set resin in the depressed portions of the printing master,
bringing the printing master, with the photo-setting resin paste being filled in the depressed portions thereof, into close contact with the print receiving material,
curing the photo-setting resin paste to make the photo-set resin in the depressed portions of the printing master by being exposed to light, and
separating the printing master from the print receiving material so as to transfer the cured photo-set resin in the depressed portions of the printing master to the print receiving material.
The first object of the present invention can also be achieved by an intaglio printing method for transferring a resin to a print receiving material, using an intaglio printing master having portions depressed in a printing shape below the surface of the printing master, the surface of the printing master except the depressed portions being coated with a light shielding layer, comprising the steps of:
filling a photo-setting resin paste that can be cured to a photo-set resin in the depressed portions of the printing master,
bringing the printing master, with the photo-setting resin paste being filled in the depressed portions thereof, into close contact with the print receiving material,
curing the photo-setting resin paste to make the photo-setting resin paste a photo-set resin in the depressed portions of the printing master by the back side of the printing master opposite to the side of the depressed portions being exposed to light, and
separating the printing master from the print receiving material so as to transfer the cured photo-set resin in the depressed portions of the printing master to the print receiving material.
The second object of the present invention can be achieved by an intaglio printer capable of transferring a resin to a print receiving material, using an intaglio printing master having portions depressed in a printing shape below the surface of the printing master, comprising:
means for filling a resin paste that can be hardened to a solid in the depressed portions of the printing master,
means for bringing the printing master, with the resin paste being filled in the depressed portions thereof, into close contact with the print receiving material,
means for hardening the resin paste to make the resin paste a hardened solid resin in the depressed portions of the printing master, and
means for separating the printing master from the print receiving material so as to transfer the hardened resin in the depressed portions of the printing master to the print receiving material.
The third object of the present invention can be achieved by a touch panel which comprises a spacer comprising an elastic material, preferably produced by any of the above-mentioned intaglio printing methods of the present invention.